The present invention relates especially but not exclusively to a liquid ring pump.
German Pat. No. DE 27 31 451 describes a liquid ring pump or compressor having a rotor floatingly mounted to the extended shaft end of the drive motor. The motor casing is so configured that operating liquid of the compressor or pump is able to circulate therein and cool the motor housing. Apart from the fact that the motor casing must be designed in a particular way, it is also necessary to provide reinforced motor shafts and shaft bearings as well as complex seals between the pump or compressor, on the one hand, and the drive motor, on the other hand, whereby the space for the seals is relatively small and inaccessible during operation.
German Pat. No. DE 26 45 305 describes a liquid ring pump and compressor having a rotor accommodated in a hermetically sealed casing, with the seals configured in the form of glands or mechanical seals. Disposed about the housing are coils to form a stator winding. As the coils are excited, a field is induced in the ferromagnetic liquid contained within the housing, thereby forming a peripheral liquid ring adhering to the interior surface of the casing. Interaction between the ring and the rotor vanes causes the rotor to turn to implement a pumping action. The drive of the rotor is thus based on a magnetic engagement of the rotor with the field. As a consequence, the use of nonmagnetic materials such as stainless steels, high alloy nickel or plastics for the rotor is precluded. However, these types of materials are in particular suitable for rotors in liquid ring pumps handling toxic and/or aggressive transport fluids. In addition, the transmission of driving forces through induction of a field has a relatively poor efficiency.
To solve these problems, German Pat. No. DE 29 12 938 discloses a liquid ring pump having a cylindrical pump housing with a rotor mounted eccentrically in the housing. An electric motor drives the pump via a canned magnetic coupling which is hermetically sealed from the pump portion by an enclosure, thereby attempting to combine better driving conditions with a hermetic seal of the pump housing. Apart from the fact that canned magnetic couplings are only suitable for pump outputs of up to about 50 KW, this conventional liquid ring pump requires numerous bearings. The interior of the pump requires two slide bearings for supporting the pump shaft on which an inner magnet carrier of the magnetic coupling is mounted. Further, two roller bearings are provided to hold an outer magnet carrier of the magnetic coupling, and two regular bearings are provided for the separate electric motor. Thus, a total of six bearings is required, resulting in a complex configuration that leads further to a relatively great structural length of the overall apparatus comprised of pump, canned magnetic coupling and electric motor. When damage occurs, in particular of the enclosure, the magnetic coupling and the supporting bearing react relatively sensitively. Thus, it is not easy to provide measures which prevent or at least substantially reduce the risk of escape of transport fluid or operating fluid of the pump, when the enclosure is damaged. In particular, when toxic and/or aggressive or expensive transport fluids are involved, an escape of such fluids is detrimental.
It would therefore be desirable and advantageous to provide an improved liquid ring pump which obviates prior art shortcomings and which is compact and simple in structure while yet reliable in operation for basically any type of operating fluid.
According to one aspect of the present invention, a liquid ring pump includes a stationary housing defining an interior space; at least one rotor mounted in the interior space on a rotor shaft for rotation in the housing; a bearing for supporting the rotor shaft in the interior space; and a drive, acting on the outer perimeter of the rotor, for driving the rotor.
The housing of the liquid ring pump may either be configured with a single interior space or split horizontally to divide the interior in several spaces, typically two spaces. This simplifies the fabrication of the housing. The rotor is suitably provided with a partition wall to separate the interior spaces.
According to another feature of the present invention, the bearings of the rotor shaft may be configured as slide bearings which are lubricated and cooled by the operating fluid. The rotor and the rotor shaft can suitably be made of a same material, for example in the form of a single-piece casting. This single-piece configuration is equally applicable for all known construction principles such as conical configuration of liquid ring pumps. There are no problems relating to gap seals between individual stages of a multi-stage liquid ring pump as the partition wall is immersed over the entire circumference in the liquid ring.
According to another feature of the present invention, the outer perimeter of the rotor may be configured as a gear wheel which projects into a bay of the housing and cooperates with a force-transmitting member of the drive in the form of a pinion which is accommodated in the bay and transmits the torque from the electric motor to the gear. The pinion is hereby lubricated by the operating fluid and has a pinion shaft which is suitably supported by slide bearings. The bay requires only one bore for passage of the pinion shaft, whereby the bore can easily be sealed by a gland or mechanical seal. Suitably, the electric motor of the drive is placed externally and has a driveshaft which is axially offset to the rotor shaft.
A liquid ring pump according to the present invention exhibits a superior efficiency compared to prior art pumps and requires a smaller torque of the drive. The useful portion of the working chamber can now be made of greater size than in conventional liquid ring pumps while maintaining same outer dimensions. Further, the rotor shaft may have a smaller diameter compared to conventional liquid ring pumps as the required drive torque is not transmitted via the rotor shaft. As a consequence of the conjointly rotating partition wall of the rotor, less frictional losses are encountered. Compared to conventional liquid ring pumps, a liquid ring pump according to the present invention requires less space and a reduced number of components. There is no need for a separate lubrication so that the liquid ring pump according to the present invention runs completely free from grease. Thus, also two-stage or multi-stage configurations as vacuum pumps and compressors are possible as differently split axial rotor halves may have varying diameters. Except for the feedthrough of the pinion shaft to the drive, the liquid ring pump according to the invention is completely hermetically sealed and only a single area (feedthrough in the bay) needs to be sealed.
According to another feature of the present invention, the rotor is driven by a device which influences the rotation speed of the liquid ring pump, with the electric motor driving the rotor via a converter or a gear mechanism. The liquid ring pump can then be utilized for a wide range of industrial processes which demand different rotation speeds, i.e. different compression conditions.
According to another feature of the present invention, an infinitely variable control of the rotation speed of a liquid ring pump according to the invention can be implemented by configuring the outer perimeter of the partition wall of the rotor in the form of a water turbine and thus to drive the rotor by a jet of a fluid such as gas or liquid, e.g. water. In this way, the rotation speed can be controlled by the applied fluid pressure or fluid amount. Configuration of such a hydrodynamic drive eliminates the need for a drive motor, thereby further reducing the dimensions of the overall liquid ring pump. Fluid pressure and fluid amount can be generated by a centrifugal pump, whereby the fluid is conducted in a closed loop or supplied from a cooling water mains if water is used as fluid. The amount of cooling water is hereby sufficient to avoid a recooling. The reservoir, typically designed as separator may, however, contain a cooling coil for recooling of the operating water. Thus, the driving water for the rotor can be used at the same time as operating water of the liquid ring pump.